The present invention relates to a method for deforming a tube near one of its ends, particularly for producing a sealed coupling for rigid tubes. The invention also relates to a tool used in such a method.
The method at issue here needs to make it possible to deform a tube in order to produce a coupling of the type depicted in FIG. 2 of document DE-195 26 316 C2 or alternatively in document DE-197 57 946 A1. These two documents disclose a coupling of a rigid pipe. A nut is pressed on to the tube that is to be coupled. The end of the tube to be coupled is introduced into a male part of the coupling which, on the one hand, on its exterior surface, has a screw thread corresponding to the tapping of the nut and, on the other hand, on its inside, has a conical bore. The tube is deformed outward to produce a shoulder that makes it possible to limit the length over which the tube to be coupled can be introduced into the male part. Once the end of the tube has been pushed into the male part, the nut is screwed on to the corresponding screw thread, bearing directly or indirectly on the deformation of the rigid tube that is to be coupled.
The cited documents do not indicate how the tube is deformed. It is in fact known practice for the end of the tube to be deformed to be placed in a die and for pressure to be exerted on the free end of the tube so as to deform its wall and for the material of which this tube is formed to be pushed into a housing provided for that purpose in the die.
One disadvantage of this device is that it entails the use of heavy duty machinery capable of exerting significant forces. Furthermore, it requires a great deal of energy to deform the tube.
Another disadvantage of this production method is that it breaks the fibers of the metal forming the tube that is to be coupled. In the region of the deformation, this tube is therefore weakened.
With other types of coupling, for which the deformation of the tube is performed immediately at the end of the tube that is to be coupled, it is known practice for the tube to be deformed by heading. Patent EP-0 381 603 B1 describes such a method for making a coupling. This method makes it possible to respect the fibers of the metal and consumes less energy but does not make it possible to produce a coupling such as those disclosed in document DE-197 57 946 A1.
An object of the present invention is therefore to provide a method which allows a tube to be deformed some distance from its free end without weakening it.
To this end, the invention proposes a method for deforming a tube having a longitudinal axis, near its end, in which method the tube is placed in an openable die having an impression corresponding to the desired final exterior shape, a free end of the tube protruding from the die.
According to the invention, this method further comprises the following steps:
introducing the end of the tube that protrudes from the die into a cavity of a form piece, this cavity having an end wall, a side wall of a shape tailored to the tube and to the desired deformation, and an opening opposite the end wall,
pressing the end of the tube against the end wall of the cavity, some clearance remaining between the opening of the cavity and the die,
applying an essentially axial force to the end of the tube via the form piece, the area of application of the force rotating about the longitudinal axis of the tube thus causing the tube to be deformed gradually,
withdrawing the end of the deformed tube from the cavity of the form piece and from the die.
The fact that the force that allows deformation to be achieved is not applied simultaneously to the entire periphery of the tube allows the tube to be deformed gradually without breaking the fibers of the metal of which this tube is made. As the tube is introduced into a cavity, the deformation is controlled. By tailoring the shape of this cavity, it is possible to leave part of the tube undeformed over a predetermined length measured from its free end.
There are various conceivable ways of exerting a force locally on the tube by rotating about the axis thereof. For example, it is conceivable to have a press roller acting on one wall of the form piece piece [sic] by rolling along this wall and describing a circle about the axis of the tube that is to be deformed.
In one advantageous embodiment of the method according to the invention, the form piece is, for example, built into a tool having a longitudinal axis that is inclined with respect to the axis of the tube and more or less secant therewith, and the essentially axial force is exerted on the end of the tube by rotating the tool, the latter then being given an orbital movement with respect to the axis of the tube, and by simultaneously bringing the tool and the die closer together.
In this embodiment, the angle of inclination between the axis of revolution of the cavity and the axis of the tube is between 2 and 5 degrees.
It is also possible to envision that a die bar, intended to rest against the interior wall of the tube to be deformed is introduced into the latter when the end of the tube is introduced into the cavity of the tool. The inside of the tube is then shaped at the same time as this tube is deformed.
In another embodiment of a method according to the invention, the form piece is placed on the end of the tube in such a way that the longitudinal axis of the cavity more or less corresponds to the longitudinal axis of the tube, and an external tool presses against an opposite face of the form piece to the face in which the cavity is made.
In this case, the external tool is advantageously a tool with an axis inclined with respect to the longitudinal axis of the tube, and this tool is given an orbital movement with respect to the longitudinal axis of the tube, combined with a movement of translation toward the die.
The present invention also relates to a tool for implementing a deforming method according to the invention. This tool it is in the form of a more or less cylindrical component, at the end of which is made an open cavity having an axis of revolution and having an end wall arranged more or less in a transverse plane and a conical region near the end wall and narrowing in the direction away from this wall. The cavity has, for example, at its open end, a second conical region connecting to the first and widening toward the open end.
To produce an annular bulge or a rib on the exterior surface of the tube that is to be deformed, the cavity advantageously has an annular groove. Likewise, to produce an annular groove on the exterior surface of the tube that is to be deformed, the cavity advantageously has an annular rib.
Another type of tool that can be used to implement a method according to the invention comprises a more or less cylindrical component, at the end of which is made an open cavity having an axis of revolution and having an end wall arranged more or less in a transverse plane and a conical region near the end wall, and it also comprises a die bar mounted to pivot with respect to a transverse axis of the cavity. This die bar allows the tube to be shaped from the inside during deformation.
In one advantageous embodiment of this type of tool, the cavity is made in a tubular piece into which the die bar fits, the end wall of the cavity being formed by the base of the die bar, these two parts being mounted in a housing of more or less circular cylindrical shape, having an end wall and open at the opposite end.